Clothing made of man-made materials has advantage over _________ made of natural ones like cotton, wool or silk.

The editor asked me to write another article for them, _____about environmental protection.

 We shouldn't take _____ for granted that we still have a lot of time before the Entrance Examination 

The chairman thought _____ necessary to invite Professor Smith to speak at the meeting.

—I'm too busy preparing the exam. Could you do _______to help me?—Of course. I can do _______for you if you want me to.